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Discussion Starter #1
I've heard these cars run just fine on the lowest grade octane (87). Is this true? Will 89 or 92 octane harm them? or will 87 or them? Thanks.
 

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White Diamond '03 DHS (with DTS floor shift)
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They were designed to run on 87 and will do so just fine. 89 or 92 will do no harm except to your wallet, but won't make any difference in performance if that is what you are looking for.
 

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2001 Deville DHS
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Ranger, would there be any difference in mpg with the higher octane?

Also most of the fuel in my area is 10% ethanol but I occasionally see some premium w/o ethanol. I have heard that ethanol reduces mpg. I am wondering if anyone has experimented with both to see if any mpg differences could justify using non-ethanol blended fuel when I come across it. I am making the assumption that my engine ('01 DHS) is otherwise indifferent to 10% ethanol blends (or not).

Thanks.
 

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White Diamond '03 DHS (with DTS floor shift)
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Higher octane will not give you any better mileage. Gas without ethanol will however.
 

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White Diamond '03 DHS (with DTS floor shift)
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Ranger per my manual it requires premium 93 Damn I sure have wasted lots of money here lately
What year do you have? Pre 2000's "recommend" premium, but will run just fine on regular. It has been discussed many times if you do a search.
 

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2007 DTS
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I am new here, but I drive 122 miles per day round trip to work. While my 2000 DTS will run on regular, I try to use mid-grade or better, whenever possible. My experience is that I get 10% better mpg with a good premium. So my rule of thumbe is that if premium is less than 10% more than regular, I go with the premium. I just completed a 900 mile trip on premium and got 24 mpg.
 

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'93 Fleetwood Brougham...Dad's
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Per GM & Cadillac, in '99 and before, the Northstar was set to run Premium and noted as such--but yes, could still run on regular like most Premium cars, it just retarded the timing to compensate.

Then with 2000, and at least through '05, the front-drive Northstar cars had revisions to allow them just to require regular 87. Again, not to say you couldn't run a higher grade as some have, but in these engines of these years, it wasn't required as earlier.

Some do find improvements on the later ones with Premium, but it all depends on the situation.
 

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The Northstar Tuner
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This is from the FSM

Document ID# 428534
2000 Cadillac DeVille


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Fuel Specifications
Use premium unleaded gasoline rated at 91 octane or higher for best performance. You may use middle grade or regular unleaded gasolines, but your vehicle may not accelerate as well.



Be sure the posted octane for premium is at least 91 (at least 89 for middle grade and 87 for regular).
If the octane is less than 87, you may get a heavy knocking noise when you drive. If it's bad enough, it can damage your engine.

If you're using fuel rated at the recommended octane or higher and you hear heavy knocking, your engine needs service. But don't worry if you hear a little pinging noise when you're accelerating or driving up a hill. That's normal, and you don't have to buy a higher octane fuel to get rid of pinging. It's the heavy, constant knock that means you have a problem.

Notice: Your vehicle was not designed for fuel that contains methanol. Do not use methanol fuel which can corrode metal parts in your fuel system and also damage plastic and rubber parts. This kind of damage would not be covered under your warranty.


Some gasolines that are not reformulated for low emissions may contain an octane-enhancing additive called methylcyclopentadienyl manganese tricarbonyl (MMT); ask your service station operator whether or not the fuel contains MMT.


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Document ID# 428534
2000 Cadillac DeVille
:D
 
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